Supertransparent high impact strength random block copolymer

ABSTRACT

A high impact strength random block copolymer including (a) about 65-97 wt. % of a crystalline propylene/ethylene copolymer A containing from about 0.5 wt. % to about 6 wt. % derived from ethylene and from about 94 wt. % to about 99.5 wt. % derived from propylene, and (b) about 3-35 wt. % of a propylene/ethylene copolymer B containing from about 8 wt. % to about 40 wt % derived from ethylene and from about 60 wt % to about 92 wt. % derived from propylene. The crystalline to amorphous ratio Lc/La of the random block copolymer ranges from about 1.00 to about 2.25. The random block copolymer is characterized by both high toughness and low haze.

BACKGROUND

1. Field of the Invention

The present invention relates to transparent high impact random blockcopolymers compositions for use in molded and extruded articles.

2. Background of the Art

A variety of transparent thermoplastic compositions have been developed,some of which have been disclosed in the patent literature and/orintroduced to the marketplace. Each of those compositions has aparticular level of transparency, often characterized in terms of“haze,” which is determined in accordance with recognized testprocedures. Shortcomings of those compositions include unsatisfactorilyhigh haze values (low transparency), poor processability and poormechanical properties, including undue hardness, low flexibility, etc.For example, previously proposed thermoplastic elastomer compositionswith transparency and flexibility such as compounds based onstyrene-ethylene-butadiene-styrene impact copolymers, thermoplasticvulcanized blends (TPV) or thermoplastic olefin (TPO) blends showtransparency and softness levels that are still unsatisfactory in someapplications.

EP 1,428,853 discloses a polypropylene polymer composition including arandom propylene-alpha-olefin copolymer, the alpha-olefin being ethyleneand one or more C₄-C₁₀ alpha-olefins. The polymer includes a matrixphase containing 2-12 mole % ethylene and a rubber phase containing25-65 mole % ethylene.

EP 1,354,901 discloses a heterophasic polypropylene composition with aMFR greater than 100 g/10 min.

WO 03/106,553 discloses high impact polypropylene copolymers with matrixand rubber present in separate phases.

WO 03/046,021 discloses a polypropylene polymer composition having a MFRof from 3 to 30 g/10 min. The polymer includes 50-90% of one or morepropylene copolymers having a xylene insoluble fraction of not less than85% and 10-50% of a propylene copolymer containing 8%-40% ethylene andoptionally 1-10 w-% of a C₄-C₈ alpha-olefin.

Other random block copolymer compositions are disclosed in EP 1,206,499,EP 373,660, EP 814,127, EP 860,457 and EP 1,162,213.

Others have attempted to make transparent compositions, but many of suchcompositions are problematic, particularly when attempting to makemolded compositions that possess a desirable combination of properties,such as softness, flexibility and strength, while also having goodprocessability. For example, others have been confronted withshortcomings in the area of processability, particularly for molded orextruded compositions, where the tendency of a material to crystallizequickly has enormous advantages. Many materials that have goodmechanical properties lack good crystallization properties. When acomposition is used for molding, it is desirable that it has a tendencyto flow well and thus quickly and easily and completely fill all areasof the mold. While there is a general tendency for higher MFR materialsto correspond to good flowability, a higher MFR is frequently alsoaccompanied by an unfortunate decrease in mechanical properties; thus ahigher MFR is not necessarily desirable for that reason. Furthermore,many compositions experience a trade-off in properties, e.g., where goodmechanical properties may be offset by poor flexibility, e.g., unduestiffness or hardness. Accordingly, there is a need for a material thathas a combination of desirable properties.

Typically, in the past one had to choose between low haze or good impactproperties. The prior art does not provide a material with both low hazeand good impact properties at the same time.

SUMMARY

A super transparent high impact strength random block copolymer isprovided herein which comprises a combination of

(a) 65-97 wt., preferably 75-97 wt. % of a crystallinepropylene/ethylene copolymer A containing from about 0.5 wt. % to about6 wt. % derived from ethylene and from about 94 wt. % to about 99.5 wt.% derived from propylene, having a melting point of 120-159° C.; and

(b) 3-35 wt. %, preferably 3-25 wt. %, of a propylene/ethylene copolymerB containing from about 8 wt. % to about 40 wt. % derived from ethyleneand from about 60 wt. % to about 92 wt. % derived from propylene,

where the random block copolymer is produced in at least a two stagereactor cascade, where copolymer A is produced in a first polymerizationreactor and copolymer B is produced in a second polymerization reactor.

The random block copolymer is characterized by an outstandingcombination of high impact strength and low haze.

DETAILED DESCRIPTION

Other than in the working examples or where otherwise indicated, allnumbers expressing amounts of materials, reaction conditions, timedurations, quantified properties of materials, and so forth, stated inthe specification are to be understood as being modified in allinstances by the term “about.”

It will also be understood that any numerical range recited herein isintended to include all sub-ranges within that range.

It will be further understood that any compound, material or substancewhich is expressly or implicitly disclosed in the specification and/orrecited in a claim as belonging to a group of structurally,compositionally and/or functionally related compounds, materials orsubstances includes individual representatives of the group and allcombinations thereof.

The present invention provides low haze (super transparent) random blockcopolymers for applications such as injection molding, sheet, film,thermoforming, blow molding and injection stretch blow molding (ISBM) bycarefully tailoring of molecular parameters.

Such parameters include:

-   -   1) the proper melt flow rate difference (delta MFR) between the        products produced in the first (copolymer A) and second        polymerization reactor (copolymer B),    -   2) the proper ethylene content of copolymer A, produced in the        first reactor,    -   3) the proper ethylene content of copolymer B, produced in the        second reactor,    -   4) the balance of the ethylene contents of copolymers A and B,    -   5) the balance of long spacing within the crystalline structure        of the random impact copolymer,    -   6) the xylene soluble (XS) content of the random block        copolymer, and    -   7) optionally adding a clarifier in the right amount to the        random impact copolymer.

Careful control and balancing of these parameters results in the growthof crystalline regions of a certain size and type, resulting in a randomblock copolymer that has an unexpectedly low haze, which is desirableyet previously thought to be impossible for impact copolymers.

Although not wishing to be limited to any theory, the low haze isbelieved to be the result of properly formed crystalline domains ofsmaller size and type than those found in typical impact copolymers.This behavior is believed to be attributable to co-crystallization ofrubber polymer chains within the matrix polymer chains. Low haze mayalso be attributed to the optimization of refractive index between thetwo phases. Smaller, more open spherulites with irregular borders incombination with very small rubber particles (D<0.5 microns) arebelieved to provide a mechanism for obtaining the combination of lowhaze and good impact properties in the random block copolymer of theinvention. Also, low molecular weight (LMW) compatible rubber tends tomigrate to the matrix domain thereby thickening the amorphous lamella(La) and thinning the crystalline lamella (Lc).

In more detail, in one embodiment of the invention a random blockcopolymer is provided herein which comprises a combination of:

(a) 65-97 wt. % of a crystalline propylene/ethylene copolymer Acontaining from about 0.5 wt. % to about 6 wt. % derived from ethyleneand from about 94 wt. % to about 99.5 wt. % derived from propylene,having a melting point (measured by means of DSC in accordance with thestandard ISO 3146) of 120-159° C.; and

(b) 3-35 wt. % of a propylene/ethylene copolymer B containing from about8 wt. % to about 40 wt. % derived from ethylene and from about 60 wt. %to about 92 wt. % derived from propylene, where the random blockcopolymer has the following properties:

-   -   (i) the propylene/ethylene copolymer B is dispersed in the        crystalline propylene/ethylene copolymer A; in a first        embodiment of the invention, the two copolymers A and B are        phase separated and in a second embodiment of the invention, the        copolymers A and B form a continuous phase random block        copolymer without phase separation,    -   (ii) in the case, the two copolymers A and B form a random block        copolymer showing phase separation, the particle size of the        dispersed polymer B is <1.5 μm, preferably <1.0 μm, particularly        preferably <0.5 μm,    -   (iii) the haze, measured in accordance with the standard ASTM D        1003 is for random block copolymers of the present invention        <12%, preferably <10%, and particularly preferably <7%.    -   (iv) the Xylene soluble fraction (XS) at 23° C., measured in        accordance with ISO Standard 16152 (Plastics-Determination of        Xylene soluble matter in Polypropylene) is 11% to about 25%,        preferably 12 to about 22, particularly 15% to about 20%,    -   (v) the MFR measured in accordance with the ISO standard 1133 at        230° C. with a load of 2.16 kg is 0.1 to about 150 dg/min,        preferably 0.5 to about 100 dg/min, particularly preferably 1 to        about 80 dg/min,    -   (vi) the ratio of powder-MFR_(random block copolymer) to the        powder-MFR_(copolymer A) are in accordance with the equation        MFR_(random block copolymer) =K(MFR_(copolymer A))        wherein K=1.0 to about 1.5, preferably 1.0 to about 1.3,        particularly preferably 1.0 to about 1.25,    -   (vii) the crystalline/amorphous ratio Lc/La, determined by small        angle X-ray scattering (SAXS), ranges from about 1.00 to about        2.25, preferably 1.25 to about 2.00, particularly preferably        1.40 to about 1.70,    -   (viii) the material optionally contains nucleating and/or        clarifying agents ranging from about 50 ppm to about 5,000 ppm,        preferably from about 100 to about 4,000 ppm, and more        preferably from about 120 to about 2,500 ppm.

Preferably, in another embodiment the random block copolymer of thepresent invention comprises a combination of:

(a) 75-95 wt. % of a crystalline propylene/ethylene copolymer Acontaining from about 1.0 wt. % to about 5 wt. %, preferably 1.5 toabout 4.5 wt. %, derived from ethylene and from about 95 wt. % to about99 wt. %, preferably 95.5 to about 98.5 wt. %, derived from propylene,having a melting point of 135-150° C., preferably of 139-146° C.; and

(b) 5-25 wt. % of a propylene/ethylene copolymer B containing from about10 wt. % to about 30 wt. %, preferably 12 to about 25 wt. %, derivedfrom ethylene and from about 70 wt. % to about 90 wt. %, preferably 75to about 88 wt. %, derived from propylene,

where the random block copolymer has the above mentioned properties(i)-(viii).

Particularly preferably, in yet another embodiment the random blockcopolymer of the present invention comprises a combination of:

(a) 80-92 wt. % of a crystalline propylene/ethylene copolymer Acontaining from about 1.5 wt. % to about 4.5 wt. %, preferably 2.0 toabout 4.0 wt. %, derived from ethylene and from about 95.5 wt. % toabout 98.5 wt. %, preferably 96 to about 98 wt. %, derived frompropylene, having a melting point of 135-150° C., preferably of 139-146°C.; and

(b) 8-20 wt. % of a propylene/ethylene copolymer B containing from about10 wt. % to about 30 wt. %, preferably 12 to about 25 wt. %, derivedfrom ethylene and from about 70 wt. % to about 90 wt. %, preferably 75wt. % to about 88 wt. %, derived from propylene,

where the random block copolymer has the above mentioned properties(i)-(viii).

Most preferably, in yet another embodiment the random block copolymer ofthe present invention comprises a combination of

(a) 88-92 wt. % of a crystalline propylene/ethylene copolymer Acontaining from about 2.0 to about 4.0 wt. %, derived from ethylene andfrom about 96 to about 98 wt. %, derived from propylene, having amelting point of 139-146° C.; and

(b) 8-12 wt. % of a propylene/ethylene copolymer B containing from about12 to about 17 wt. %, derived from ethylene and from about 83 to about88 wt. %, derived from propylene,

where the random block copolymer has the above mentioned properties(i)-(viii).

The polymers of the invention can be produced using any coordinatingcatalyst, like single-site catalysts or Ziegler-Natta catalysts, theZiegler-Natta catalyst being preferred.

The method of the present invention includes preparing a random blockcopolymer by sequential polymerization. Ethylene and propylene arecopolymerized in a first reaction zone to provide a propylene-ethylenecopolymer component A of the impact copolymer of the invention.Component A is then sent to a second reaction zone where ethylene andpropylene are copolymerized to provide the component B which isincorporated into the polymer. The ethylene content of component A canrange from about 0.5 wt. % to about 6 wt. % and the propylene contentcan range from 94 wt. % to about 99.5 wt. %. Component B of the impactcopolymer contains from about 8 wt % to about 40 wt. % of ethylene and60 wt. % to about 92 wt. % of propylene.

Random block copolymers of the present invention can be produced inslurry polymerization processes conducted in inert hydrocarbon solvents,bulk polymerization processes conducted in liquefied propylene, in gasphase polymerization processes or in processes, where the abovementioned processes are combined. As an example., in a first stepcopolymer A can be produced in a bulk process and copolymer B can beproduced in a gas phase process. Gas phase processes with a fluidized orstirred bed are preferable, especially a two reactor system wherein thecopolymer A is made in the first reactor and the copolymer B in thesecond reactor. Such a process provides for in situ blending of the twocopolymer components A and B to form a block copolymer, which isnecessary, as compared to a physical blending of the copolymercomponents A and B which does not produce an impact copolymer of thepresent invention.

The catalysts for use in such systems include Ziegler-Natta catalystsand single site catalysts.

Ziegler-Natta catalysts, including titanium-based catalysts, aredescribed in U.S. Pat. Nos. 4,376,062, 4,379,758 and 5,066,737.Ziegler-Natta catalysts typically are magnesium/titanium/electron donorcomplexes, optionally supported on a suitable support like silica, usedin conjunction with an organoaluminum cocatalyst and an externalselectivity control agent such as an aromatic carboxylic acid ester oran alkoxy silane compound.

Single site catalysts, e.g., metallocene catalysts, compriseorganometallic coordination complexes of one or more ligands inassociation with a metal atom and are described, for example, in U.S.Pat. No. 7,169,864.

In accordance with the process, discrete portions of the catalystcomponents are continuously fed to the reactor in catalyticallyeffective amounts together with the monomers propylene and ethylenewhile the polymer product is continuously removed during the continuingprocess. Polymerization technologies useful for this purpose aredescribed e.g., in Polypropylene Handbook, 2nd edition, p. 361 ff.(Hanser Publishers, Munich 2005).

The polymerization is generally carried out at temperatures of from 20to 150° C. and at pressures of from 1 to 100 bar, with average residencetimes of from 0.5 to 5 hours, preferably at temperatures of from 60 to90° C. and at pressures of from 10 to 50 bar, with average residencetimes of from 0.5 to 3 hours. The polymerization can be carried outbatchwise or, preferably, continuously.

For example, in the first reactor a mixture of propylene and ethylene isintroduced together with hydrogen, catalyst, organoaluminum cocatalystand external selectivity control agent. The amount of hydrogen to thecombined monomers propylene and ethylene is in the range of about 10 toabout 200 g hydrogen/metric ton (mt) monomers, preferably about 20 toabout 100 g hydrogen/mt monomers, most preferably about 30 to about 60 ghydrogen/mt monomers if a Ziegler-Natta catalyst is used or in the rangeof about 0.05 to about 20 g hydrogen/mt monomer and is preferably about0.1 to about 10 g hydrogen/mt monomer if a metallocene catalyst is used.

A mixture of copolymer A with active catalyst embedded in the polymermatrix is produced in the first reactor. This mixture from the firstreactor is transferred to the second reactor to which no additionalsolid catalyst need be added. Additional cocatalyst and/or externalselectivity control agent optionally may be added to the second reactor.In the second reactor, propylene and ethylene are maintained at a gasphase composition in a range of mole ratio of about 0.10 to about 0.50moles of ethylene per mole of propylene, and preferably about 0.12 toabout 0.30 moles of ethylene per mole propylene. In order to regulatethe molecular weight of the copolymer B, hydrogen (H₂) is introduced inthe second reactor in an amount of 100-500 g/mt of propylene, preferably200-400 g/mt of propylene and most preferably 250-350 g/mt of propylene.Such a process creates the random block copolymer of the presentinvention containing the copolymer A and the copolymer B.

The random block copolymer of the invention preferably contains aclarifying agent in an amount ranging from about 50 ppm to about 5,000ppm, preferably from about 100 to about 4,000 ppm, and more preferablyfrom about 120 to about 2,500 ppm.

Of such clarifying agents, dibenzylidene sorbitol type clarifying agentsare preferred, including, but not limited to, dibenzylidene sorbitolclarifiers having alkyl, alkoxy or halogen substituents on either orboth aromatic rings, whereby the alkyl substituents can be C₁ to C₂₀,and may be branched, linear or cycloalkyl, and combinations of suchsorbitol derivatives. Some specific examples of same arebis(3,5-dimethyl benzylidene)sorbitol, bis(p-ethyl benzylidene)sorbitol,bis(p-methyl benzylidene)sorbitol and combinations thereof. Suchclarifying agents are commercially available as MILLAD 3940 and 3988from Milliken Chemical Co. of Spartanburg, S.C.; NC-4 from Mitsui ToatsuChemicals, Inc. of Tokyo, Japan; Uniplex CX 45-56 from Unitex ChemicalCorp., Greensboro, N.C.; and Geniset MD from New Japan Chemical Co.,Tokyo, Japan.

Other possible clarifying agents are Millad NX 8000 (Milliken Co);Irgaclear XT 386 (Ciba Specialty Chemicals Inc., Basel, Switzerland);Ricaclear PC 1 (Rika International, Manchester, UK); ADK-STAB NA-21 andADK-STAB NA-71 (Asahi Denka, Tokyo, Japan).

The compositions of the invention may also contain additives such asthermal stabilizers, antioxidants, lubricants, acid scavengers,synergists, anti-static agents, nucleating additives and additives whichstabilize against radiation, such as ultraviolet (UV) stabilizers andthose that provide resistance to gamma irradiation.

Antioxidants include the sub-classes of primary and secondaryantioxidants; examples of primary antioxidants include the phenolic-typeadditives typified by IRGANOX 1010, IRGANOX 3114 (Ciba) or ETHANOX 330(Albemarle). Their main function is to provide long-term thermalstability such as is usually needed in fabricated articles.

The class of secondary antioxidants includes additives that containphosphorus in either organophosphite or organophosphoniteconfigurations. Examples of such phosphites include IRGAFOS 168 orIRGAFOS 12 (Ciba), ULTRANOX 626, ULTRANOX 627A, ULTRANOX 641 (Chemtura),DOVERPHOS S-9228 (Dover Chemical Co.).

Organophosphonite secondary antioxidants are typified by IRGAFOS P-EPQ(Ciba). Other secondary antioxidants are exemplified by lower molecularweight phenolic-types such as BHT or IRGANOX 1076, or high molecularweight hydroxyl amines such as IRGASTAB FS 042 (Ciba). Secondaryantioxidants function mainly by providing stability in melt flow andcolor during the melt processing of the plastic material. Another classof secondary antioxidants comprises the benzofuranone (lactone)derivatives as represented by IRGANOX HP-136 (Ciba).

Lubricants or mold release agents are typified by fatty acid amides,examples of which include ethylene bis-(stearamide, oleamide anderucamide).

Acid scavengers may be categorized as salts of fatty acids, e.g. stearicacid or lactic acid salts and related derivatives, hydrotalcite-likecompounds, and certain metal oxides. Examples of each type in orderinclude calcium stearate, zinc stearate, calcium lactate, DHT-4A (KyowaChemical Co. Tokyo, Japan), and zinc or magnesium oxides. Synergistsenhance the performance of primary antioxidants. Examples include thethioesters of fatty acids typified by Di-stearyl-thio-dipropionate(DSTDP), Di-lauryl-thio-dipropionate (DLTDP) andDi-myristyl-thio-dipropionate (DMTDP).

Anti-static agents enhance static charge decay on molded parts. Keyexamples include glyceryl monostearate and glyceryl distearate, as wellas mixtures thereof.

Nucleating additives are typically benzoic acid salts such as sodium,lithium or aluminum benzoate, minerals such as micronized talc, andorganophosphorous salts such as ADK-STAB NA-11 or ADK-STAB NA-25 (AsahiDenka).

Ultraviolet stabilization is provided by light absorbers such as TINUVIN327 (Ciba) or by hindered amine type stabilizers such as CYASORB 3346(Cytec Industries Inc.), TINUVIN 622, TINUVIN 770 DF or CHIMASSORB 944(Ciba).

Resistance against gamma irradiation is provided by combinations ofadditives such as phosphorous-containing secondary antioxidants andhindered amines. Additionally, Milliken's RS 200 additive is of benefit,as are other mobilizing additives such as mineral oil (cited in U.S.Pat. Nos. 4,110,185 and 4,274,932).

Preferred antioxidants include1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxy-benzyl)benzene(A); octadecyl 3-(3′,5′-di-tert-butyl-4′-hydroxyphenyl)propionate (B);tetrakis[methylene(3,5-di-tert-butyl-4-hydroxyhydrocinnamate)]methane(C); tris[3,5-di-t-butyl-4-hydroxybenzyl)isocyanurate (D);3,5-di-tert-butyl-4-hydroxyhydrocinnamic acid triester with1,3,5-tris(2-hydroxyethyl)-s-triazine-2,4,6(1H,3H,5H)-trione (E);1,3,5-tris-(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl)1,3,5-triazine-2,4,6-(1H,3H,5H)-trione (F);bis-[3,3-bis(4-hydroxy-3-tert-butyl-phenyl)-butanoic acid]-glycolester(G); 2,2′-methylene-bis-(4-methyl-6-tertiary-butylphenol)-terephthalate(H); and 2,2bis[4-(2-(3,5-di-tert-butyl-4-hydroxyhydrocinnamoyloxy))ethoxy-phenyl]propane(1); calciumbis[monoethyl(3,5-di-tert-butyl-4-hydroxybenzyl)phosphonate](J);1,2-bis(3,5-di-tert-butyl-4-hydroxyhydrocinnamoyl)hydrazine (K); and2,2-oxamido bis[ethyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate](L).

Additional additives may be used separately or blended with the abovelisted antioxidants. This applies to all the above additive types andfurther includes fillers like talc, calcium carbonate, barium sulfate,clays, silicates, pigments, such as titanium dioxide, zinc oxide, leadchromate, cadmium sulfides, cadmium selenide, zinc sulfide, basiccarbonate of white lead; flame retardants such as antimony oxide;ultra-violet stabilizers, slip agents, anti-impact agents, and otheradditives which enhance the properties and processability of the randomblock copolymer to which they are added.

While the above listing seeks to provide key examples of the differentadditive types, it is not to be viewed as limited by the examples inscope. It is also recognized that certain of the above additives aremulti-functional, e.g., an acid acceptor such as calcium stearate mayalso provide mold release performance, as may also be the case withglycerol monostearate. Further, combinations of any or all types ofadditives given, or of additives within a given class, are considered tobe within the scope of the present invention.

The random impact block copolymer of the present invention may besubjected to a chemical degradation treatment (visbreaking or clipping)according to processes well known in the art, in order to improve theflowability and to obtain the required MFR values (measured according toISO standard 1133). The chemical degradation of the copolymer is carriedout in the presence of a free radical initiator, such as organicperoxide. Examples of free radical initiators that can be used for thispurpose are e.g. Di-t-butyl-peroxide,(2,5-Dimethyl-2,5-ditert-butylperoxy)-hexane or3,6,9-Triethyl-3,6,9-trimethyl-1,4,7-triperoxononane.

The random block copolymers of the present invention may be used in anystandard molded products in which similar polyolefin resins andconventional polypropylene impact copolymers are used. However, theadded advantage of good stiffness and high toughness in combination withoutstanding clarity expands this range of utility over standard impactcopolymers, such that the random block copolymers of the presentinvention can be used in food and non-food containers, drinking cups,water bottles, caps & closures, medical devices and toys where the needfor clarity otherwise restricts use to either random propylene-ethylenecopolymers of inherently lower toughness or to other polymers such aspolycarbonate, which while tough, are several times more expensive. Theneed for toughness at freezer temperatures, combined with stiffness andclarity, is met by the materials of this invention at lower cost.

According to the present invention, random block copolymers with low hothexane solubles content, determined in accordance with FDA 177.1520, canbe produced, enabling them to be used for cooking applications. Inaddition, according to the present invention, random block copolymerscan be produced which can be sterilized for medical application by steamautoclaving or gamma irradiation. In addition, such grades can be usedfor microwave heating and cooking.

METHODS

The following test methods were used in the Examples given below.

XS (Xylene Soluble Fraction) was determined at 23° C. according to ISO16152.

Xylene solubles are defined as the percent by weight remaining insolution after the polymer sample is dissolved in hot Xylene andsubsequent cooling down of the solution to 23° C. The difference betweenXylene solubles after the second stage of polymerization and the firststage of polymerization largely correlates to the rubber content of therubber content of the random block copolymers of the present invention.

MFR (Melt Flow Rate) was determined in accordance with ISO 1133 at 230°C. with a load of 2.16 kg. According to this measurement, the MFR refersto the weight of the polymer extruded through a standard cylindrical dieat a standard temperature of 230° C. in a laboratory apparatus carryinga standard piston and load of 2.16 kg. The MFR is a measure of the meltviscosity of a polymer and hence of its molar mass.

Haze was determined in accordance with ASTM D 1003 using test specimenswith a dimension of 6×6 cm and a thickness of 1 mm. These plates havebeen injection molded at a mold temperature of 210° C. and a toolsurface temperature of 40° C. The tool has to be carefully polished toguarantee a glossy and scratch free surface of the test plates produced.After a storage time of 48 hours at room temperature to ensure themaximum possible crystallization of the polymer, the measurement wasmade at 23° C. using a Gretag Macbeth Color-Eye 7000A spectrophotometer.The test specimens are measured in the center of the plate. Haze ismeasured as a percentage of transmitted light that is scattered morethan 2.5 degrees from the direction of the incident beam. The reportedhaze value is the average result of the individual haze values measuredon three different plates. The lower the haze % numbers, the higher isthe transparency of the test specimen. Materials with haze valuesgreater than 30% are considered to be diffusing.

The glass transition temperature (Tg) was determined by means oftorsional Dynamic Mechanical Analysis (DMA) on compression moldedrectangular bars in accordance with ASTM D 4065-06. Temperature andfrequency dependent tests were made using a Rheometrics Dynamic AnalyzerRDA II. Pellet samples for each material were melted and moulded in formof a sheet of uniform thickness (1 mm) in a laboratory hot press at 200°C. and 20 MPa for 7 min, followed by cooling (inside the press) for 11min; the cooling water temperature was 15° C.

The test specimens were cut from the compression molded sheets in thefollowing dimensions: length 30 mm, width 10 mm, and thickness 1 mm.They were then kept at 23° C. and 50% r.h. for a minimum length of timeof 88 h (ISO 291) before carrying out the measurements.

The samples were subjected to a sinusoidal strain of 0.3% (to ensureviscolelastic behavior) at a constant frequency of 1 rad/s. Thetemperature dependence of the dynamic mechanical loss tangent, tan δ,was measured from −150° C. up to 80° C. at an average heating rate of 3°C./min under a nitrogen atmosphere. Finally the glass transitiontemperature of each sample was defined as the peak of the tan δ curve asa function of temperature (tan δ is defined as the ratio of the lossmodulus E″ to the storage modulus E′).

The melting point (Tm) was determined by DSC in accordance with ISOstandard 3146 using a 5 mg polymer sample and applying a first heatingstep at a heating rate of 20° C./min up to 230° C. and a hold at 230° C.for 10 min, followed by a crystallization step with a cooling rate of20° C./min from 200° C. to −20° C. with a hold at −20° C. of 10 min,followed by a second heating step at a heating rate of 20° C./min to230° C. The reported melting point is the temperature, where theenthalpy of the second heating cycle displays the maximum. Instrumentsfrom Perkin Elmer (DSC 7) and TA Instruments (Q 1000 DSC) have been usedafter calibration with Indium under the above mentioned measurementconditions.

The hexane soluble content (HS) was determined in accordance with FDA177.1520 by using 2 g of a respective film of 2 mil thickness made ofthe polymer. The film was extracted at 50° C. for 2 hours. After theextraction, the hexane extract was separated into a flask and thecontent of extracted polymer was gravimetrically determined afterremoval of the hexane under reduced pressure.

The ethylene content of the copolymers was determined by FT-IR (FourierTransform Infra red Spectroscopy). The test method is suitable for thequantitative determination of the ethylene content in propylene-ethylenecopolymers. The method employs calibrations based on sets of referencesamples covering a suitable range of ethylene levels. The ethylenecontent of these reference samples was determined by ¹³C NMR.

A small amount of resin is placed in a spacer frame, sandwiched betweenpolyester film, and molded into a film of 200±10 microns thickness at210° C. and 200 bar for 10 min, then cooled down to <40° C. underpressure.

The test samples are then exposed to the probe of the FT-IR spectrometerand the spectra are recorded in the relevant wave number range(absorption bands of the ethylene in the impact copolymers: 720-730cm⁻¹)

Spectra are transformed into the format suitable to be analysed by thechemometry software package. The chemometrical analysis of the FT-IRdata results in the ethylene content of the sample in percent.

The impact strength was measured by notched or un-notched Charpy test oninjection moulded specimens according to ISO 179-1(Plastics—Determination of Charpy impact properties Part 1: Instrumentedimpact test)

Small Angle X-Ray Scattering (SAXS) was performed on injection-moldedplaques to determine long spacing (Lp) crystalline spacing (Lc) andamorphous spacing (La) quantities in the tested copolymers. The spacingwas obtained by profile fitting the peak in the SAXS data with apseudo-Voigt function (Jade version 7, Materials Data Inc., Livermore,Calif.) in which the skew was refined. The background was determined bytwo straight lines determined by the high and low angle linearscattering limits. The data were collected on a line source system(Rigaku Ultima 3). The system was configured with a multilayer mirror,0.03 micron first slit and second 1 mm slit set to reduce the parasiticscatter from the mirror and the beam defining slits. The diffracted beamside of the system consisted of a vacuum pathway, scatter slit of 0.2 mmand detector slit of 0.01 mm. Data were collected at 6 seconds/step with0.005 degrees per step.

The tests indicated above were performed on Example 1, ComparativeExamples A, B, and C, and the commercially available clarified randomcopolymers indicated herein.

EXAMPLES

Various features of the invention are illustrated by Example 1 below.The Comparative Examples and commercial products tested do not representthe invention but are presented for comparison purposes.

All products mentioned in Table 1 were produced by a stirred gas phaseprocess in a reactor cascade consisting of two 25 m³ gas phase reactorswith helical stirrers.

Example 1 as well as the comparative examples A, B and C are randomblock copolymers, consisting of a crystalline propylene/ethylenecopolymer A, produced in the first stirred gas phase reactor and apropylene/ethylene copolymer B, produced in the second stirred gas phasereactor of the cascade.

In the first reactor, a mixture of propylene and ethylene was introducedtogether with hydrogen, ZN-catalyst, organoaluminum cocatalyst and anexternal donor (Silane).

Temperature, pressure and the feed ratios for ethylene and hydrogen withrespect to the propylene feed are given in Table 1. After an averageresidence time of 60 min, a mixture of copolymer A with active catalystembedded in the polymer matrix was transferred to the second reactorwithout adding additional catalyst. In the second reactor, thepolymerization of the copolymer B was taking place at reduced pressureand temperature (see table 1), again at a residence time of 60 min.

The products were stabilized stabilized/additivated by blending thepolymer powder from the second reactor (powder MFR's between 1.7 and 2.5as indicated in Table 1) with a combination of Irgafos 168 (secondaryanti-oxidant), Irganox 1010 (primary anti-oxidant), Calcium stearate(acid scavenger), Glycerol monostearate (GMS) (anti-static agent) andMillad 3988 (clarifier).

They were subsequentially visbroken by2,5-dimethyl-2,5-di(tert-butylperoxy)hexane to MFR's between 12 and 15(see Table 1) and pelletized on a Werner & Pfleiderer corotating doublescrew extruder.

TABLE 1 (Example 1, comparative examples A, B and C and commercialcomparative examples 3240 NC and 3348 SC) Polimerization ParametersExample 1 Comp. Ex. A Comp. Ex. B Comp. Ex. C 3240NC 3348SC 1st ReactorPressure Barg 24 24 24 24 24 24 Temperature ° C. 75 75 75 75 75 75 C2Feed Ratio Kg 38 28 28 26 28 38 C2/tnC3 H2 Feed Ratio g H2/tnC3 44 40 4032 38 46 Powder C2 wt-% 3 2.2 2.2 1.8 2.2 3 content Powder MFR g/10 min1.4 1.95 1.95 1.3 1.8 1.5 XS % 8.5 6.5 6.5 6.0 6.5 8.5 2nd ReactorPressure Barg 12.5 12.5 12.5 12.5 — — Temperature ° C. 69 69 69 69 — —C2 Feed Ratio Kg 50 50 50 80 — — C2/tnC3 C3 Feed Ton C3/h 0.3 0.3 0 0 —— H2 Feed Ratio g H2/tnC3 295 160 160 530 — — Powder MFR g/10 min 1.71.8 1.8 2.5 — — Δ MFR_(R2-R1) g/10 min 0.3 −0.15 −0.15 1.2 — — FinalProduct Final MFR pellets g/10 min 12 15 15 15 12 25 Final XS % 17.215.5 16.2 20.6 — — Ratio 1st/2nd wt:wt 91:9 91:9 90:10 85:15 — — ReactorFinal Product Properties Haze % 5.8 15 20 15 11 11 Tg ° C. −9 −6 −6−6/−50 −5 −5 Tm ° C. 142 147 146 151 150 145 Hexane solubles (%) 4.2 4.23.8 — 2.2 3.2 IS Charpy notched (KJ/m²) 29 11 11 40 6 6.3 @ 23° C. ISCharpy (KJ/m²) 5 6 6 8 2 3.5 notched @ 0° C. IS Charpy (KJ/m²) 1 1 1 1 11 notched @ −20° C. IS Charpy (KJ/m²) NB NB NB NB 200 NB @ 23° C. ISCharpy (KJ/m²) NB NB NB NB 100 180 @ 0° C. IS Charpy (KJ/m²) NB NB NB NB17 50 @ −20° C. Flexural Modulus MPa 590 700 710 770 1050 740 NB:without break

Example 1

Example 1 was produced in a two step process. In the first stage, apropylene/ethylene random copolymer with 3 wt-% ethylene content waspolymerized in gas phase. In the second stage, a low molecular weightpropylene/ethylene rubber, rich in propylene was polymerized.

In order to obtain a low molecular weight rubber, a proper amount ofhydrogen was added to the second reactor. As a result of this, a K-value(the ratio of the second reactor powder MFR to the first reactor powderMFR) of 1.21 was achieved.

In order to have a rubber phase rich in propylene, an additional amountof propylene was injected in the second stage of polymerization.

The ratio between the propylene/ethylene random copolymer and thepropylene/ethylene rubber in the final product was 91:9 (parts byweight).

The polymer powder obtained in the polymerization was admixed with astandard additive mixture in the extrusion step. The polymer wascompounded in a twin screw extruder at 250° C. The polymer compositionobtained contained 0.1% by weight of Irgafos 168 (from Ciba SC), 0.05%by weight of frganox 1010 (from Ciba SC), 0.11% by weight of CalciumStearate (from Baerlocher), 0.06% by weight of Atmer 122 (from Ciba SC)and 0.2% by weight of Millad 3988 (from Milliken Chemical).

For visbreaking from the powder melt flow rate of 1.7 g/10 min to thefinal pellet melt flow rate of about 12 g/10 min,2,5-dimethyl-2,5-di(tert-butylperoxy)hexane was used.

Other operative conditions and general properties of the producedpolymer are indicated in Table 1 above.

COMPARATIVE EXAMPLES Comparative Example A

Comparative Example A was produced in a two step process. In the firststage, a propylene/ethylene random copolymer with 2.2 wt-% ethylene waspolymerized in gas phase. A composition of propylene/ethylene rubbersimilar to Example 1 was polymerized in the second stage. In thiscomparative example, a lower amount of hydrogen was injected, in orderto obtain a higher molecular weight of the rubber phase. As aconsequence, a K value (the ratio of the second reactor powder MFR tothe first reactor powder MFR) lower than 1 was achieved.

The ratio between the propylene/ethylene random copolymer and thepropylene/ethylene rubber was 91:9 (parts by weight).

The polymer powder obtained in the polymerization was admixed with astandard additive mixture in the extrusion step. The polymer wascompounded in a twin screw extruder at 250° C. The polymer compositionobtained contained 0.1% by weight of Irgafos 168 (from Ciba SC), 0.05%by weight of Irganox 1010 (from Ciba SC), 0.11% by weight of calciumstearate (from Baerlocher), 0.06% by weight of Atmer 122 (from Ciba SC)and 0.2% by weight of Millad 3988 (from Milliken Chemical).

For visbreaking from the powder melt flow rate of 1.8 g/10 min to thefinal melt flow rate of 15 g/10 min,2,5-dimethyl-2,5-di(tert-butylperoxy)hexane was used.

In Comparative Example A, as a result of a lower amount of ethylene inthe first stage composition (random copolymer) and a higher molecularweight in the second stage polymerization (rubber phase), the resultinghaze was higher compared to the one achieved in Example 1.

Other operative conditions of the produced polymer are indicated inTable 1.

Comparative Example B

Comparative Example B was produced in a two step process. In the firststage, a propylene/ethylene random copolymer with 2.2 w-% ethylene waspolymerized in gas phase. In this comparative example, the same amountof hydrogen was injected as in Comparative Example A, in order to obtaina similar molecular weight of the rubber phase (higher than in Example1). As a consequence, a K-value lower than 1 was achieved.

Comparative Example B was produced without the injection of propylene inthe second reactor, in order to achieve a different composition in therubber phase.

The ratio between the propylene/ethylene random copolymer and thepropylene/ethylene rubber was 90:10 (parts by weight).

The polymer powder obtained in the polymerization was admixed with astandard additive mixture in the extrusion step. The polymer wascompounded in a twin screw extruder at 250° C. The polymer compositionobtained contained 0.1% by weight of Irgafos 168 (from Ciba SC), 0.05%by weight of Irganox 1010 (from Ciba SC), 0.11% by weight of calciumstearate (from Baerlocher), 0.06% by weight of Atmer 122 (from Ciba SC)and 0.2% by weight of Millad 3988 (from Milliken Chemical).

For visbreaking from the powder melt flow rate of 1.8 g/10 min to thefinal melt flow rate of 15 g/10 min,2,5-dimethyl-2,5-di(ter-butylperoxy)hexane was used.

In Comparative Example B, as a result of a lower amount of ethylene inthe first stage composition (random copolymer), a higher molecularweight in the second stage polymerization (rubber phase), and a moreincompatible rubber phase due to its chemical composition, the resultinghaze was higher compared to the one achieved in Comparative Example A.

Other operative conditions of the produced polymer are indicated abovein Table 1.

Comparative Example C

Comparative Example C was produced in a two step process stirred gasphase process. In the first stage, a propylene/ethylene random copolymerwith an ethylene content of 1.8 wt-% was polymerized in gas phase.Comparative Example C was produced without the injection of propylene,but with a higher amount of hydrogen in the second reactor. As aconsequence, a K-value (the ratio of the second reactor powder MFR tothe first reactor powder MFR) of 1.92 was achieved, which was higherthan in Example 1.

The ratio between the propylene/ethylene random copolymer and thepropylene/ethylene rubber was 85:15 (parts by weight).

The polymer powder obtained in the polymerization was admixed with astandard additive mixture in the extrusion step. The polymer wascompounded in a twin screw extruder at 250° C. The polymer compositionobtained contained 0.1% by weight of Irgafos 168 (from Ciba SC), 0.05%by weight of Irganox 1010 (from Ciba SC), 0.11% by weight of calciumstearate (from Baerlocher), 0.06% by weight of Atmer 122 (from Ciba SC)and 0.2% by weight of Millad 3988 (from Milliken Chemical).

For visbreaking from the powder melt flow rate of 2.5 g/10 min to thefinal melt flow fate of 15 g/10 min,2,5-dimethyl-2,5-di(tert-butylperoxy)hexane was used.

In spite of having a positive ΔMFR_(R2-R1) (very low molecular weight ofthe rubber phase), the resulting haze of the product of ComparativeExample C was higher than that achieved in Example 1 as a result of alower amount of ethylene in the random copolymer of the first stage, anda more incompatible rubber phase in the second stage of thepolymerization.

Other operative conditions of the produced polymer are indicated inTable 1.

COMMERCIAL COMPARATIVE EXAMPLES

3240NC and 3348SC are designations of random copolymers commerciallyavailable from Novolen Technology.

3240NC and 3348SC were both produced in a single gas phase reactor.3240NC is a propylene/ethylene random copolymer with 2.2 wt-% ethylene.3348 SC is a propylene/ethylene random copolymer with 3 wt-% ethylene.

The polymer powder obtained in the polymerization was admixed with astandard additive mixture in the extrusion step. The polymers werecompounded in a twin screw extruder at 250° C. The polymer compositionof 3240 NC contained 0.1% by weight of Irgafos 168 (from Ciba SC), 0.05%by weight of frganox 1010 (from Ciba SC), 0.11% by weight of calciumstearate (from Baerlocher), 0.06% by weight of Atmer 122 (from Ciba SC)and 0.2% by weight of Millad 3988 (from Milliken Chemical) as clarifyingagent. 3348 SC contains additionally 0.2% Atmer 122 as antielectrostaticagent.

For visbreaking from the powder melt flow rate to the final melt flowrate of about 12 g/10 min for 3240NC and 25 g/10 min for 3348SC,2,5-dimethyl-2,5-di(tert-butylperoxy)hexane was used.

Examples presented in Table 1 clearly show that only by carefullytailoring molecular parameters, such as matrix ethylene content, rubbercomposition and rubber molecular weight, a very low haze value can beobtained by adding a rubber phase to a random copolymer matrix.

Careful control and balancing of those parameters results in the growthof crystalline regions of a certain size and type, resulting in anrandom block copolymer that has an unexpectedly low haze, which isdesirable yet previously thought to be impossible for impact copolymers.

Table 2 shows this fact, where contrary to conventional expectations,increasing rubber content, as shown by increasing XS values, can resultin lower haze values.

Starting from a random copolymer with a haze value of about 11%, theincorporation of a properly designed rubber phase leads to an increasingimprovement in transparency while the amount of such rubber phase,measured by the Xs content, is increased. In this way and following thepolymerization parameters already presented in Example 1 (Table 1) itwas possible to achieve a final haze about half the starting value.There are no significant changes in product melting point since therandom copolymer matrix has the same ethylene content.

TABLE 2 Haze reduction by rubber incorporation to a Random copolymermatrix XS (%) Haze (%) Tm (° C.) Start Random 8.5 11.0 143 12.6 10.0 14312.8 9.2 143 14.4 8.3 142 15.3 6.0 142 16.9 5.8 142 Example 1 17.2 5.8142

Although not wishing to be limited to any theory, the low haze isbelieved to be the result of properly formed crystalline domains ofsmaller size and type than those found in typical random copolymers.This behavior is believed to be attributable to co-crystallization ofrubber chains within the matrix chains. Smaller, more open spheruliteswith irregular borders in combination with very small rubber particles(<0.4 μm) are believed to provide a mechanism for obtaining the uniquebalance of low haze and good impact properties in the random blockcopolymer of the invention. Also, low molecular weight (LMW) compatiblerubber tends to migrate to the matrix domain thereby thickening theamorphous lamella (La) and thinning the crystalline lamella (Lc). Thiseffect is presented in Table 3.

TABLE 3 Crystalline to Amorphous Long Haze (%) Spacing Ratio (Lc/La)Spacing Lp (Å) Example 1 5.8 1.5 129 3240NC 11 2.3 139

The random block copolymer of the invention (Example 1) has smaller longspacing (Lp) and lower crystalline to amorphous spacing ratio (Lc/La),which correlates to a decrease in haze. These results suggest that thestructure of copolymer A and the presence of copolymer B of the presentinvention tend to reduce the size of crystallites by disrupting theirstructure through co-crystallization.

While the above description contains many specifics, these specificsshould not be construed as limitations of the invention, but merely asexemplifications of preferred embodiments thereof. Those skilled in theart will envision many other embodiments within the scope and spirit ofthe invention as defined by the claims appended hereto.

1. A method of making a random block copolymer comprising: a)introducing into a first reaction zone a polymerization catalyst and afirst feed containing from about 0.5 parts by weight to about 6 parts byweight of ethylene and from about 94 parts by weight to about 99.5 partsby weight propylene; b) copolymerizing the ethylene and propylene underfirst polymerization reaction conditions to provide a copolymer A withactive catalyst embedded therein; c) introducing the copolymer A into asecond reaction zone; d) introducing to the second reaction zone asecond feed containing from about 8 parts by weight to about 40 parts byweight of ethylene and from about 60 parts by weight to about 92 partsby weight propylene; e) copolymerizing the ethylene and propylene of thesecond feed to provide a copolymer B wherein the copolymer B iscopolymerized with the copolymer A under second polymerization reactionconditions and in such proportion as to provide a random block copolymercontaining from about 75 wt. % to about 95 wt. % blocks of copolymer Aand about 5 wt. % to about 25 wt. % blocks of copolymer B.
 2. The methodof claim 1 wherein: the first feed contains from about 1 parts by weightto about 5 parts by weight of ethylene and from about 95 parts by weightto about 99 parts by weight propylene, the second feed contains fromabout 10 parts by weight to about 30 parts by weight of ethylene andfrom about 70 parts by weight to about 90 parts by weight propylene, andthe random block copolymer contains from about 75 wt. % to about 95 wt.% blocks of copolymer A and about 5 wt. % to about 25 wt. % blocks ofcopolymer B.
 3. The method of claim 1 wherein: the first feed containsfrom about 1.5 parts by weight to about 4.5 parts by weight of ethyleneand from about 95.5 parts by weight to about 98.5 parts by weightpropylene, the second feed contains from about 10 parts by weight toabout 30 parts by weight of ethylene and from about 70 parts by weightto about 90 parts by weight propylene, and the random block copolymercontains from about 80 wt. % to about 92 wt. % blocks of copolymer A andabout 8 wt. % to about 20 wt. % blocks of copolymer B.
 4. The method ofclaim 1 wherein the first feed contains from about 2 parts by weight toabout 4 parts by weight of ethylene and from about 96 parts by weight toabout 98 parts by weight propylene, the second feed contains from about12 parts by weight to about 17 parts by weight of ethylene and fromabout 83 parts by weight to about 88 parts by weight propylene, and therandom block copolymer contains from about 88 wt. % to about 92 wt. %blocks of copolymer A and about 8 wt. % to about 12 wt. % blocks ofcopolymer B.
 5. The method of claim 1 wherein the catalyst is aZiegler-Natta catalyst or metallocene catalyst.
 6. The method of claim 1wherein both the first polymerization reaction and the secondpolymerization reaction are carried out in a stirred bed gas phaseprocess.
 7. The method of claim 1 wherein the first polymerizationreaction is a bulk polymerization process conducted in liquefiedpropylene.
 8. The method of claim 7 wherein the second polymerizationreaction is a gas phase process and the second reaction zone includes afluidized bed or stirred bed.
 9. The method of claim 1 wherein the firstand/or second polymerization reaction conditions include a temperatureof from 20 to 150° C., a pressure of from 1 to 100 bar, and an averageresidence time of from 0.5 to 5 hours.
 10. The method of claim 1 whereinthe first and/or second polymerization reaction conditions include atemperatures of from 60 to 90° C., a pressure of from 10 to 50 bar, andan average residence time of from 0.5 to 3 hours.
 11. The method ofclaim 2 further comprising the introduction of hydrogen into the firstand/or second polymerization reaction zone.
 12. The method of claim 1wherein the polymerization catalyst comprises a Ziegler-Natta catalyst.13. A method of making a random block copolymer comprising: a)introducing into a first reaction zone a polymerization catalyst and afirst feed containing from about 0.5 parts by weight to about 6 parts byweight of ethylene and from about 94 parts by weight to about 99.5 partsby weight propylene; b) copolymerizing the ethylene and propylene underfirst polymerization reaction conditions to provide a copolymer A withactive catalyst embedded therein; c) introducing the copolymer A into asecond reaction zone; d) introducing to the second reaction zone asecond feed containing from about 8 parts by weight to about 40 parts byweight of ethylene and from about 60 parts by weight to about 92 partsby weight propylene; e) copolymerizing the ethylene and propylene of thesecond feed to provide a copolymer B wherein the copolymer B iscopolymerized with the copolymer A under second polymerization reactionconditions and in such proportion as to provide a random block copolymercontaining from about 65 wt. % to about 97 wt. % blocks of copolymer Aand about 3 wt. % to about 35 wt. % blocks of copolymer B; and whereinthe polymerization catalyst comprises a Ziegler-Natta catalyst.